PERSISTANT ELEVATION OF INTRACELLULAR CALCIUM IN HIPPOCAMPAL NEURONS DURING THE LATENCY PERIOD FOLLOWING STATUS EPILEPTICUS IN THE PILOCARPINE MODEL OF EPILEPTOGENEIS
Abstract number :
2.076
Submission category :
Year :
2003
Submission ID :
4007
Source :
www.aesnet.org
Presentation date :
12/6/2003 12:00:00 AM
Published date :
Dec 1, 2003, 06:00 AM
Authors :
Mohsin Raza, Robert Blair, Sompong Sombati, Robert DeLorenzo Neurology, Virginia Commonwealth University, Richmond, VA; Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, VA; Molecular Biophysics and Biochemistry, Virginia Commonweal
The prolonged elevation of intracellular calcium following the injury that induces epileptogenesis (ie. status epilepticus, stroke) has been implicated in mediating the long term changes associated with the development of epilepsy (Proc. Natl. Acad. Sci. 1998;95:14482; Brain Res.1999;851:20.). However, it has not previously been possible to test whether calcium remains elevated following SE in an in vivo model of epilepsy. This study was intitiated to acutely isolate neurons from hippocampal slices prepared from epileptic and control animals immediately after SE, during the latency period and up to one year following SE in the pilocarpine model of epileptogenesis.
SE was induced by pilocarpine injection and animals were sacrificed and hippocampal neurons were acutely isolated from hippocampal slices obtained from control and SE animals at different time intervals following SE for up to one year (Brain Res.2001;903:1). Following isolation the neurons were loaded with calcium indicator dies (Fura-2 or Fura-FF) and intracellular calcium levels were determined using a high speed fluorescence imaging system (Brain Res.2001;903:1).
Immediately following SE the mean intracellular hippocampal calcium levels exceeded 2 uM and for control cells was 112 nM. At 24 hours after SE the mean intracellular hippocampal calcium level was 659 nM and 128nM in control cells. The mean intracellular hippocampal calcium levels at 2, 6, 10, and 14 days after SE were 508 nM, 275 nM, 246 nM, and 237 nM in comparison to control animals sacrificed at the same time points with levels of 113 nM, 125 nM, 118 nM, and 126 nM. The elevations in incracellular calcium levels observed at these time points after SE were significantly different from the control levels (p[lt]0.01). Thus, intracellular calcium levels were significantly elevated during the entire latency period following SE. Intracellular calcium levels never completely returned to control levels and the levels at 1, 6, and 12 months after SE were still significantly elevated above age matched controls (p[lt]0.01).
The results from this study provide the first direct evidence in an in vivo model of epileptogenesis that intracellular hippocampal neuronal calcium is significantly elevated immediately following SE, during the latency period, and essentially for the life of the epileptic animal. The data suggest that significantly elevated calcium levels may play a role in the induction (latency period) and maintenance of epileptogenesis.
[Supported by: NIH-NINDS grants P50NS25630 and R01NS23350.]